My father-in-law is attempting to follow his dream of retiring to the road with a concession trailer (soup and sandwich wagon). He's building his trailer from scratch, but he's not confident with electricity so asked for my help.
We're looking at several scenarios: somewhere with full 50A service, lesser 30A service, or being dry and running on one or two portable generators (thinking 3-4kW each). I'm trying to design an AC power system around this.
My thought is to divide the electrical loads into two groups (#1, critical and #2, convenience), and put each group on its own distribution panel. The external power connector would be 240v50a, with one leg servicing each panel, so only 120v in a panel (and a separate drop for a 240v outlet, though I don't know why he wants that). Which is well and good, if you have a 50A service.
If running on two generators, we'll have an adapter that has two 30a inlets, each attached to one leg of the 50a side. So we end up with common neutral/ground, and each generator powers its own panel. I don't anticipate anything as fancy as phase-matched generators, so that 240v outlet will be useless.
Finally, on one gen or a 30a service, we use the same Y-adapter to power only the #1 panel. But here, I got to thinking that we could tie the two panels together, using a reverse-rated breaker, thus powering the #2 panel as well -- with obvious limits on how much stuff you can actually use.
That last bit creates a couple of hazards. First, the "empty" leg of the Y-adapter (with exposed male contacts) will be live, unless you remember to open the main breaker on the #2 panel. Second, if you then relocate where you have 50a service and forget to open the tie breaker, you're going to make a big spark as soon as you plug in -- but the tie breaker should trip almost instantly. But even this problem could be solved if the breaker handles are chained together such that closing one automatically opens the other. Hmm.
I made a rough sketch (attached). It's shown as two boxes, but it could be done in a single split-phase panel. Also not sure if the 50a receptacle breaker is needed here.
I'm planning on having separate ground and neutral buses, NOT bonded anywhere within the trailer, only at the service point. If running two generators, maybe bond the frames together? Trailer frame will be bonded to ground. Now, I'm not sure if it's proper to also frame-ground the DC power system...?
Thoughts? I doubt the NEC would approve, but practical safety is pretty high on my list of priorities.
CA Traveler, if you re-read my post, you'll find that I already mentioned all of your concerns: "creates a couple of hazards" (I wouldn't have mentioned the live male plug if I didn't think it was a problem). "Trailer frame will be bonded to ground." "could be done in a single split-phase panel". And if you look at the sketch, it shows a single 50a 4-wire shore connection. We'll use plug adapters as needed.
You're very right about the live male plug. Much better to spend a few extra dollars for a single 30-50a adapter when only one 30a service is available. The 30-50a dual "cheater" adapter is only for using dual generators. Even then it's important that one generator doesn't feed power to the other, hence the idea of chaining the tie and #2 main breaker handles together so that you can't close both at the same time. A poor man's transfer switch, you see.
I don't know anything about load-shedding devices. A quick search turns up mainly complaints about them. I'm not finding a lot of confidence there.
Finally, this is an early sketch, I haven't really sat down to figure out what the loads are yet. The #2 side might end up just being a 2nd AC, or a soup warmer or a fryer...in which case cross-tying a 30a supply would be useless anyway, so we forget it and we're back to a very conventional panel. We'll see.
Is he going to insure this unit?Will it be inspected and a permit to operate and sell food need to be issued at some time,health inspectors etc. involved and so on?You may need to really have him think this thing through and check regulations that may need to be addressed at any venue or function.
Where is he going to be using this concession trailer?
If he is going to be selling items at organized events there is a good probability that he will face a health inspection. In some places this could include things like the requirements for the number of sinks, etc. Need to design for these inspections.
Also at some of these events the fire department will also inspect the vendors trailers. If the electrical is not up to code they may not allow him to operate.
Also has he checked into insurance? At a minimum he needs business liability insurance. It may be required by the event organizer. What happens if something goes wrong and customers get sick, perhaps some form of food poisoning? Without insurance he could have a major problem.